app.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// @dart = 2.8

import 'dart:ui' as ui;

import 'package:flutter/cupertino.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';

import 'arc.dart';
import 'colors.dart';
import 'floating_action_button.dart';
import 'icons.dart';
import 'material_localizations.dart';
import 'page.dart';
import 'theme.dart';

/// [MaterialApp] uses this [TextStyle] as its [DefaultTextStyle] to encourage
/// developers to be intentional about their [DefaultTextStyle].
///
/// In Material Design, most [Text] widgets are contained in [Material] widgets,
/// which sets a specific [DefaultTextStyle]. If you're seeing text that uses
/// this text style, consider putting your text in a [Material] widget (or
/// another widget that sets a [DefaultTextStyle]).
const TextStyle _errorTextStyle = TextStyle(
  color: Color(0xD0FF0000),
  fontFamily: 'monospace',
  fontSize: 48.0,
  fontWeight: FontWeight.w900,
  decoration: TextDecoration.underline,
  decorationColor: Color(0xFFFFFF00),
  decorationStyle: TextDecorationStyle.double,
  debugLabel: 'fallback style; consider putting your text in a Material',
);

/// Describes which theme will be used by [MaterialApp].
enum ThemeMode {
  /// Use either the light or dark theme based on what the user has selected in
  /// the system settings.
  system,

  /// Always use the light mode regardless of system preference.
  light,

  /// Always use the dark mode (if available) regardless of system preference.
  dark,
}

/// An application that uses material design.
///
/// A convenience widget that wraps a number of widgets that are commonly
/// required for material design applications. It builds upon a [WidgetsApp] by
/// adding material-design specific functionality, such as [AnimatedTheme] and
/// [GridPaper].
///
/// The [MaterialApp] configures the top-level [Navigator] to search for routes
/// in the following order:
///
///  1. For the `/` route, the [home] property, if non-null, is used.
///
///  2. Otherwise, the [routes] table is used, if it has an entry for the route.
///
///  3. Otherwise, [onGenerateRoute] is called, if provided. It should return a
///     non-null value for any _valid_ route not handled by [home] and [routes].
///
///  4. Finally if all else fails [onUnknownRoute] is called.
///
/// If a [Navigator] is created, at least one of these options must handle the
/// `/` route, since it is used when an invalid [initialRoute] is specified on
/// startup (e.g. by another application launching this one with an intent on
/// Android; see [Window.defaultRouteName]).
///
/// This widget also configures the observer of the top-level [Navigator] (if
/// any) to perform [Hero] animations.
///
/// If [home], [routes], [onGenerateRoute], and [onUnknownRoute] are all null,
/// and [builder] is not null, then no [Navigator] is created.
///
/// {@tool snippet}
/// This example shows how to create a [MaterialApp] that disables the "debug"
/// banner with a [home] route that will be displayed when the app is launched.
///
/// ![The MaterialApp displays a Scaffold ](https://flutter.github.io/assets-for-api-docs/assets/material/basic_material_app.png)
///
/// ```dart
/// MaterialApp(
///   home: Scaffold(
///     appBar: AppBar(
///       title: const Text('Home'),
///     ),
///   ),
///   debugShowCheckedModeBanner: false,
/// )
/// ```
/// {@end-tool}
///
/// {@tool snippet}
/// This example shows how to create a [MaterialApp] that uses the [routes]
/// `Map` to define the "home" route and an "about" route.
///
/// ```dart
/// MaterialApp(
///   routes: <String, WidgetBuilder>{
///     '/': (BuildContext context) {
///       return Scaffold(
///         appBar: AppBar(
///           title: const Text('Home Route'),
///         ),
///       );
///     },
///     '/about': (BuildContext context) {
///       return Scaffold(
///         appBar: AppBar(
///           title: const Text('About Route'),
///         ),
///       );
///      }
///    },
/// )
/// ```
/// {@end-tool}
///
/// {@tool snippet}
/// This example shows how to create a [MaterialApp] that defines a [theme] that
/// will be used for material widgets in the app.
///
/// ![The MaterialApp displays a Scaffold with a dark background and a blue / grey AppBar at the top](https://flutter.github.io/assets-for-api-docs/assets/material/theme_material_app.png)
///
/// ```dart
/// MaterialApp(
///   theme: ThemeData(
///     brightness: Brightness.dark,
///     primaryColor: Colors.blueGrey
///   ),
///   home: Scaffold(
///     appBar: AppBar(
///       title: const Text('MaterialApp Theme'),
///     ),
///   ),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
///  * [Scaffold], which provides standard app elements like an [AppBar] and a [Drawer].
///  * [Navigator], which is used to manage the app's stack of pages.
///  * [MaterialPageRoute], which defines an app page that transitions in a material-specific way.
///  * [WidgetsApp], which defines the basic app elements but does not depend on the material library.
///  * The Flutter Internationalization Tutorial,
///    <https://flutter.dev/tutorials/internationalization/>.
class MaterialApp extends StatefulWidget {
  /// Creates a MaterialApp.
  ///
  /// At least one of [home], [routes], [onGenerateRoute], or [builder] must be
  /// non-null. If only [routes] is given, it must include an entry for the
  /// [Navigator.defaultRouteName] (`/`), since that is the route used when the
  /// application is launched with an intent that specifies an otherwise
  /// unsupported route.
  ///
  /// This class creates an instance of [WidgetsApp].
  ///
  /// The boolean arguments, [routes], and [navigatorObservers], must not be null.
  const MaterialApp({
    Key key,
    this.navigatorKey,
    this.home,
    this.routes = const <String, WidgetBuilder>{},
    this.initialRoute,
    this.onGenerateRoute,
    this.onGenerateInitialRoutes,
    this.onUnknownRoute,
    this.navigatorObservers = const <NavigatorObserver>[],
    this.builder,
    this.title = '',
    this.onGenerateTitle,
    this.color,
    this.theme,
    this.darkTheme,
    this.highContrastTheme,
    this.highContrastDarkTheme,
    this.themeMode = ThemeMode.system,
    this.locale,
    this.localizationsDelegates,
    this.localeListResolutionCallback,
    this.localeResolutionCallback,
    this.supportedLocales = const <Locale>[Locale('en', 'US')],
    this.debugShowMaterialGrid = false,
    this.showPerformanceOverlay = false,
    this.checkerboardRasterCacheImages = false,
    this.checkerboardOffscreenLayers = false,
    this.showSemanticsDebugger = false,
    this.debugShowCheckedModeBanner = true,
    this.shortcuts,
    this.actions,
  }) : assert(routes != null),
       assert(navigatorObservers != null),
       assert(title != null),
       assert(debugShowMaterialGrid != null),
       assert(showPerformanceOverlay != null),
       assert(checkerboardRasterCacheImages != null),
       assert(checkerboardOffscreenLayers != null),
       assert(showSemanticsDebugger != null),
       assert(debugShowCheckedModeBanner != null),
       routeInformationProvider = null,
       routeInformationParser = null,
       routerDelegate = null,
       backButtonDispatcher = null,
       super(key: key);

  /// Creates a [MaterialApp] that uses the [Router] instead of a [Navigator].
  const MaterialApp.router({
    Key key,
    this.routeInformationProvider,
    @required this.routeInformationParser,
    @required this.routerDelegate,
    this.backButtonDispatcher,
    this.builder,
    this.title = '',
    this.onGenerateTitle,
    this.color,
    this.theme,
    this.darkTheme,
    this.highContrastTheme,
    this.highContrastDarkTheme,
    this.themeMode = ThemeMode.system,
    this.locale,
    this.localizationsDelegates,
    this.localeListResolutionCallback,
    this.localeResolutionCallback,
    this.supportedLocales = const <Locale>[Locale('en', 'US')],
    this.debugShowMaterialGrid = false,
    this.showPerformanceOverlay = false,
    this.checkerboardRasterCacheImages = false,
    this.checkerboardOffscreenLayers = false,
    this.showSemanticsDebugger = false,
    this.debugShowCheckedModeBanner = true,
    this.shortcuts,
    this.actions,
  }) : assert(routeInformationParser != null),
       assert(routerDelegate != null),
       assert(title != null),
       assert(debugShowMaterialGrid != null),
       assert(showPerformanceOverlay != null),
       assert(checkerboardRasterCacheImages != null),
       assert(checkerboardOffscreenLayers != null),
       assert(showSemanticsDebugger != null),
       assert(debugShowCheckedModeBanner != null),
       navigatorObservers = null,
       navigatorKey = null,
       onGenerateRoute = null,
       home = null,
       onGenerateInitialRoutes = null,
       onUnknownRoute = null,
       routes = null,
       initialRoute = null,
       super(key: key);

  /// {@macro flutter.widgets.widgetsApp.navigatorKey}
  final GlobalKey<NavigatorState> navigatorKey;

  /// {@macro flutter.widgets.widgetsApp.home}
  final Widget home;

  /// The application's top-level routing table.
  ///
  /// When a named route is pushed with [Navigator.pushNamed], the route name is
  /// looked up in this map. If the name is present, the associated
  /// [WidgetBuilder] is used to construct a [MaterialPageRoute] that performs
  /// an appropriate transition, including [Hero] animations, to the new route.
  ///
  /// {@macro flutter.widgets.widgetsApp.routes}
  final Map<String, WidgetBuilder> routes;

  /// {@macro flutter.widgets.widgetsApp.initialRoute}
  final String initialRoute;

  /// {@macro flutter.widgets.widgetsApp.onGenerateRoute}
  final RouteFactory onGenerateRoute;

  /// {@macro flutter.widgets.widgetsApp.onGenerateInitialRoutes}
  final InitialRouteListFactory onGenerateInitialRoutes;

  /// {@macro flutter.widgets.widgetsApp.onUnknownRoute}
  final RouteFactory onUnknownRoute;

  /// {@macro flutter.widgets.widgetsApp.navigatorObservers}
  final List<NavigatorObserver> navigatorObservers;

  /// {@macro flutter.widgets.widgetsApp.routeInformationProvider}
  final RouteInformationProvider routeInformationProvider;

  /// {@macro flutter.widgets.widgetsApp.routeInformationParser}
  final RouteInformationParser<Object> routeInformationParser;

  /// {@macro flutter.widgets.widgetsApp.routerDelegate}
  final RouterDelegate<Object> routerDelegate;

  /// {@macro flutter.widgets.widgetsApp.backButtonDispatcher}
  final BackButtonDispatcher backButtonDispatcher;

  /// {@macro flutter.widgets.widgetsApp.builder}
  ///
  /// Material specific features such as [showDialog] and [showMenu], and widgets
  /// such as [Tooltip], [PopupMenuButton], also require a [Navigator] to properly
  /// function.
  final TransitionBuilder builder;

  /// {@macro flutter.widgets.widgetsApp.title}
  ///
  /// This value is passed unmodified to [WidgetsApp.title].
  final String title;

  /// {@macro flutter.widgets.widgetsApp.onGenerateTitle}
  ///
  /// This value is passed unmodified to [WidgetsApp.onGenerateTitle].
  final GenerateAppTitle onGenerateTitle;

  /// Default visual properties, like colors fonts and shapes, for this app's
  /// material widgets.
  ///
  /// A second [darkTheme] [ThemeData] value, which is used to provide a dark
  /// version of the user interface can also be specified. [themeMode] will
  /// control which theme will be used if a [darkTheme] is provided.
  ///
  /// The default value of this property is the value of [ThemeData.light()].
  ///
  /// See also:
  ///
  ///  * [themeMode], which controls which theme to use.
  ///  * [MediaQueryData.platformBrightness], which indicates the platform's
  ///    desired brightness and is used to automatically toggle between [theme]
  ///    and [darkTheme] in [MaterialApp].
  ///  * [ThemeData.brightness], which indicates the [Brightness] of a theme's
  ///    colors.
  final ThemeData theme;

  /// The [ThemeData] to use when a 'dark mode' is requested by the system.
  ///
  /// Some host platforms allow the users to select a system-wide 'dark mode',
  /// or the application may want to offer the user the ability to choose a
  /// dark theme just for this application. This is theme that will be used for
  /// such cases. [themeMode] will control which theme will be used.
  ///
  /// This theme should have a [ThemeData.brightness] set to [Brightness.dark].
  ///
  /// Uses [theme] instead when null. Defaults to the value of
  /// [ThemeData.light()] when both [darkTheme] and [theme] are null.
  ///
  /// See also:
  ///
  ///  * [themeMode], which controls which theme to use.
  ///  * [MediaQueryData.platformBrightness], which indicates the platform's
  ///    desired brightness and is used to automatically toggle between [theme]
  ///    and [darkTheme] in [MaterialApp].
  ///  * [ThemeData.brightness], which is typically set to the value of
  ///    [MediaQueryData.platformBrightness].
  final ThemeData darkTheme;

  /// The [ThemeData] to use when 'high contrast' is requested by the system.
  ///
  /// Some host platforms (for example, iOS) allow the users to increase
  /// contrast through an accessibility setting.
  ///
  /// Uses [theme] instead when null.
  ///
  /// See also:
  ///
  ///  * [MediaQueryData.highContrast], which indicates the platform's
  ///    desire to increase contrast.
  final ThemeData highContrastTheme;

  /// The [ThemeData] to use when a 'dark mode' and 'high contrast' is requested
  /// by the system.
  ///
  /// Some host platforms (for example, iOS) allow the users to increase
  /// contrast through an accessibility setting.
  ///
  /// This theme should have a [ThemeData.brightness] set to [Brightness.dark].
  ///
  /// Uses [darkTheme] instead when null.
  ///
  /// See also:
  ///
  ///  * [MediaQueryData.highContrast], which indicates the platform's
  ///    desire to increase contrast.
  final ThemeData highContrastDarkTheme;

  /// Determines which theme will be used by the application if both [theme]
  /// and [darkTheme] are provided.
  ///
  /// If set to [ThemeMode.system], the choice of which theme to use will
  /// be based on the user's system preferences. If the [MediaQuery.platformBrightnessOf]
  /// is [Brightness.light], [theme] will be used. If it is [Brightness.dark],
  /// [darkTheme] will be used (unless it is null, in which case [theme]
  /// will be used.
  ///
  /// If set to [ThemeMode.light] the [theme] will always be used,
  /// regardless of the user's system preference.
  ///
  /// If set to [ThemeMode.dark] the [darkTheme] will be used
  /// regardless of the user's system preference. If [darkTheme] is null
  /// then it will fallback to using [theme].
  ///
  /// The default value is [ThemeMode.system].
  ///
  /// See also:
  ///
  ///  * [theme], which is used when a light mode is selected.
  ///  * [darkTheme], which is used when a dark mode is selected.
  ///  * [ThemeData.brightness], which indicates to various parts of the
  ///    system what kind of theme is being used.
  final ThemeMode themeMode;

  /// {@macro flutter.widgets.widgetsApp.color}
  final Color color;

  /// {@macro flutter.widgets.widgetsApp.locale}
  final Locale locale;

  /// {@macro flutter.widgets.widgetsApp.localizationsDelegates}
  ///
  /// Internationalized apps that require translations for one of the locales
  /// listed in [GlobalMaterialLocalizations] should specify this parameter
  /// and list the [supportedLocales] that the application can handle.
  ///
  /// ```dart
  /// import 'package:flutter_localizations/flutter_localizations.dart';
  /// MaterialApp(
  ///   localizationsDelegates: [
  ///     // ... app-specific localization delegate[s] here
  ///     GlobalMaterialLocalizations.delegate,
  ///     GlobalWidgetsLocalizations.delegate,
  ///   ],
  ///   supportedLocales: [
  ///     const Locale('en', 'US'), // English
  ///     const Locale('he', 'IL'), // Hebrew
  ///     // ... other locales the app supports
  ///   ],
  ///   // ...
  /// )
  /// ```
  ///
  /// ## Adding localizations for a new locale
  ///
  /// The information that follows applies to the unusual case of an app
  /// adding translations for a language not already supported by
  /// [GlobalMaterialLocalizations].
  ///
  /// Delegates that produce [WidgetsLocalizations] and [MaterialLocalizations]
  /// are included automatically. Apps can provide their own versions of these
  /// localizations by creating implementations of
  /// [LocalizationsDelegate<WidgetsLocalizations>] or
  /// [LocalizationsDelegate<MaterialLocalizations>] whose load methods return
  /// custom versions of [WidgetsLocalizations] or [MaterialLocalizations].
  ///
  /// For example: to add support to [MaterialLocalizations] for a
  /// locale it doesn't already support, say `const Locale('foo', 'BR')`,
  /// one could just extend [DefaultMaterialLocalizations]:
  ///
  /// ```dart
  /// class FooLocalizations extends DefaultMaterialLocalizations {
  ///   FooLocalizations(Locale locale) : super(locale);
  ///   @override
  ///   String get okButtonLabel {
  ///     if (locale == const Locale('foo', 'BR'))
  ///       return 'foo';
  ///     return super.okButtonLabel;
  ///   }
  /// }
  ///
  /// ```
  ///
  /// A `FooLocalizationsDelegate` is essentially just a method that constructs
  /// a `FooLocalizations` object. We return a [SynchronousFuture] here because
  /// no asynchronous work takes place upon "loading" the localizations object.
  ///
  /// ```dart
  /// class FooLocalizationsDelegate extends LocalizationsDelegate<MaterialLocalizations> {
  ///   const FooLocalizationsDelegate();
  ///   @override
  ///   Future<FooLocalizations> load(Locale locale) {
  ///     return SynchronousFuture(FooLocalizations(locale));
  ///   }
  ///   @override
  ///   bool shouldReload(FooLocalizationsDelegate old) => false;
  /// }
  /// ```
  ///
  /// Constructing a [MaterialApp] with a `FooLocalizationsDelegate` overrides
  /// the automatically included delegate for [MaterialLocalizations] because
  /// only the first delegate of each [LocalizationsDelegate.type] is used and
  /// the automatically included delegates are added to the end of the app's
  /// [localizationsDelegates] list.
  ///
  /// ```dart
  /// MaterialApp(
  ///   localizationsDelegates: [
  ///     const FooLocalizationsDelegate(),
  ///   ],
  ///   // ...
  /// )
  /// ```
  /// See also:
  ///
  ///  * [supportedLocales], which must be specified along with
  ///    [localizationsDelegates].
  ///  * [GlobalMaterialLocalizations], a [localizationsDelegates] value
  ///    which provides material localizations for many languages.
  ///  * The Flutter Internationalization Tutorial,
  ///    <https://flutter.dev/tutorials/internationalization/>.
  final Iterable<LocalizationsDelegate<dynamic>> localizationsDelegates;

  /// {@macro flutter.widgets.widgetsApp.localeListResolutionCallback}
  ///
  /// This callback is passed along to the [WidgetsApp] built by this widget.
  final LocaleListResolutionCallback localeListResolutionCallback;

  /// {@macro flutter.widgets.widgetsApp.localeResolutionCallback}
  ///
  /// This callback is passed along to the [WidgetsApp] built by this widget.
  final LocaleResolutionCallback localeResolutionCallback;

  /// {@macro flutter.widgets.widgetsApp.supportedLocales}
  ///
  /// It is passed along unmodified to the [WidgetsApp] built by this widget.
  ///
  /// See also:
  ///
  ///  * [localizationsDelegates], which must be specified for localized
  ///    applications.
  ///  * [GlobalMaterialLocalizations], a [localizationsDelegates] value
  ///    which provides material localizations for many languages.
  ///  * The Flutter Internationalization Tutorial,
  ///    <https://flutter.dev/tutorials/internationalization/>.
  final Iterable<Locale> supportedLocales;

  /// Turns on a performance overlay.
  ///
  /// See also:
  ///
  ///  * <https://flutter.dev/debugging/#performanceoverlay>
  final bool showPerformanceOverlay;

  /// Turns on checkerboarding of raster cache images.
  final bool checkerboardRasterCacheImages;

  /// Turns on checkerboarding of layers rendered to offscreen bitmaps.
  final bool checkerboardOffscreenLayers;

  /// Turns on an overlay that shows the accessibility information
  /// reported by the framework.
  final bool showSemanticsDebugger;

  /// {@macro flutter.widgets.widgetsApp.debugShowCheckedModeBanner}
  final bool debugShowCheckedModeBanner;

  /// {@macro flutter.widgets.widgetsApp.shortcuts}
  /// {@tool snippet}
  /// This example shows how to add a single shortcut for
  /// [LogicalKeyboardKey.select] to the default shortcuts without needing to
  /// add your own [Shortcuts] widget.
  ///
  /// Alternatively, you could insert a [Shortcuts] widget with just the mapping
  /// you want to add between the [WidgetsApp] and its child and get the same
  /// effect.
  ///
  /// ```dart
  /// Widget build(BuildContext context) {
  ///   return WidgetsApp(
  ///     shortcuts: <LogicalKeySet, Intent>{
  ///       ... WidgetsApp.defaultShortcuts,
  ///       LogicalKeySet(LogicalKeyboardKey.select): const ActivateIntent(),
  ///     },
  ///     color: const Color(0xFFFF0000),
  ///     builder: (BuildContext context, Widget child) {
  ///       return const Placeholder();
  ///     },
  ///   );
  /// }
  /// ```
  /// {@end-tool}
  /// {@macro flutter.widgets.widgetsApp.shortcuts.seeAlso}
  final Map<LogicalKeySet, Intent> shortcuts;

  /// {@macro flutter.widgets.widgetsApp.actions}
  /// {@tool snippet}
  /// This example shows how to add a single action handling an
  /// [ActivateAction] to the default actions without needing to
  /// add your own [Actions] widget.
  ///
  /// Alternatively, you could insert a [Actions] widget with just the mapping
  /// you want to add between the [WidgetsApp] and its child and get the same
  /// effect.
  ///
  /// ```dart
  /// Widget build(BuildContext context) {
  ///   return WidgetsApp(
  ///     actions: <Type, Action<Intent>>{
  ///       ... WidgetsApp.defaultActions,
  ///       ActivateAction: CallbackAction(
  ///         onInvoke: (Intent intent) {
  ///           // Do something here...
  ///           return null;
  ///         },
  ///       ),
  ///     },
  ///     color: const Color(0xFFFF0000),
  ///     builder: (BuildContext context, Widget child) {
  ///       return const Placeholder();
  ///     },
  ///   );
  /// }
  /// ```
  /// {@end-tool}
  /// {@macro flutter.widgets.widgetsApp.actions.seeAlso}
  final Map<Type, Action<Intent>> actions;

  /// Turns on a [GridPaper] overlay that paints a baseline grid
  /// Material apps.
  ///
  /// Only available in checked mode.
  ///
  /// See also:
  ///
  ///  * <https://material.io/design/layout/spacing-methods.html>
  final bool debugShowMaterialGrid;

  @override
  _MaterialAppState createState() => _MaterialAppState();

  /// The [HeroController] used for Material page transitions.
  ///
  /// Used by the [MaterialApp].
  static HeroController createMaterialHeroController() {
    return HeroController(
      createRectTween: (Rect begin, Rect end) {
        return MaterialRectArcTween(begin: begin, end: end);
      },
    );
  }
}

class _MaterialScrollBehavior extends ScrollBehavior {
  @override
  TargetPlatform getPlatform(BuildContext context) {
    return Theme.of(context).platform;
  }

  @override
  Widget buildViewportChrome(BuildContext context, Widget child, AxisDirection axisDirection) {
    // When modifying this function, consider modifying the implementation in
    // the base class as well.
    switch (getPlatform(context)) {
      case TargetPlatform.iOS:
      case TargetPlatform.linux:
      case TargetPlatform.macOS:
      case TargetPlatform.windows:
        return child;
      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
        return GlowingOverscrollIndicator(
          child: child,
          axisDirection: axisDirection,
          color: Theme.of(context).accentColor,
        );
    }
    return null;
  }
}

class _MaterialAppState extends State<MaterialApp> {
  HeroController _heroController;

  bool get _usesRouter => widget.routerDelegate != null;

  @override
  void initState() {
    super.initState();
    _heroController = MaterialApp.createMaterialHeroController();
  }

  // Combine the Localizations for Material with the ones contributed
  // by the localizationsDelegates parameter, if any. Only the first delegate
  // of a particular LocalizationsDelegate.type is loaded so the
  // localizationsDelegate parameter can be used to override
  // _MaterialLocalizationsDelegate.
  Iterable<LocalizationsDelegate<dynamic>> get _localizationsDelegates sync* {
    if (widget.localizationsDelegates != null)
      yield* widget.localizationsDelegates;
    yield DefaultMaterialLocalizations.delegate;
    yield DefaultCupertinoLocalizations.delegate;
  }

  Widget _inspectorSelectButtonBuilder(BuildContext context, VoidCallback onPressed) {
    return FloatingActionButton(
      child: const Icon(Icons.search),
      onPressed: onPressed,
      mini: true,
    );
  }

  Widget _materialBuilder(BuildContext context, Widget child) {
    // Resolve which theme to use based on brightness and high contrast.
    final ThemeMode mode = widget.themeMode ?? ThemeMode.system;
    final Brightness platformBrightness = MediaQuery.platformBrightnessOf(context);
    final bool useDarkTheme = mode == ThemeMode.dark
      || (mode == ThemeMode.system && platformBrightness == ui.Brightness.dark);
    final bool highContrast = MediaQuery.highContrastOf(context);
    ThemeData theme;

    if (useDarkTheme && highContrast && widget.highContrastDarkTheme != null) {
      theme = widget.highContrastDarkTheme;
    } else if (useDarkTheme && widget.darkTheme != null) {
      theme = widget.darkTheme;
    } else if (highContrast && widget.highContrastTheme != null) {
      theme = widget.highContrastTheme;
    }
    theme ??= widget.theme ?? ThemeData.light();

    return AnimatedTheme(
      data: theme,
      isMaterialAppTheme: true,
      child: widget.builder != null
        ? Builder(
            builder: (BuildContext context) {
              // Why are we surrounding a builder with a builder?
              //
              // The widget.builder may contain code that invokes
              // Theme.of(), which should return the theme we selected
              // above in AnimatedTheme. However, if we invoke
              // widget.builder() directly as the child of AnimatedTheme
              // then there is no Context separating them, and the
              // widget.builder() will not find the theme. Therefore, we
              // surround widget.builder with yet another builder so that
              // a context separates them and Theme.of() correctly
              // resolves to the theme we passed to AnimatedTheme.
              return widget.builder(context, child);
            },
          )
        : child,
    );
  }

  Widget _buildWidgetApp(BuildContext context) {
    // The color property is always pulled from the light theme, even if dark
    // mode is activated. This was done to simplify the technical details
    // of switching themes and it was deemed acceptable because this color
    // property is only used on old Android OSes to color the app bar in
    // Android's switcher UI.
    //
    // blue is the primary color of the default theme.
    final Color materialColor = widget.color ?? widget.theme?.primaryColor ?? Colors.blue;
    if (_usesRouter) {
      return WidgetsApp.router(
        key: GlobalObjectKey(this),
        routeInformationProvider: widget.routeInformationProvider,
        routeInformationParser: widget.routeInformationParser,
        routerDelegate: widget.routerDelegate,
        backButtonDispatcher: widget.backButtonDispatcher,
        builder: _materialBuilder,
        title: widget.title,
        onGenerateTitle: widget.onGenerateTitle,
        textStyle: _errorTextStyle,
        color: materialColor,
        locale: widget.locale,
        localizationsDelegates: _localizationsDelegates,
        localeResolutionCallback: widget.localeResolutionCallback,
        localeListResolutionCallback: widget.localeListResolutionCallback,
        supportedLocales: widget.supportedLocales,
        showPerformanceOverlay: widget.showPerformanceOverlay,
        checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages,
        checkerboardOffscreenLayers: widget.checkerboardOffscreenLayers,
        showSemanticsDebugger: widget.showSemanticsDebugger,
        debugShowCheckedModeBanner: widget.debugShowCheckedModeBanner,
        inspectorSelectButtonBuilder: _inspectorSelectButtonBuilder,
        shortcuts: widget.shortcuts,
        actions: widget.actions,
      );
    }

    return WidgetsApp(
      key: GlobalObjectKey(this),
      navigatorKey: widget.navigatorKey,
      navigatorObservers: widget.navigatorObservers,
      pageRouteBuilder: <T>(RouteSettings settings, WidgetBuilder builder) {
        return MaterialPageRoute<T>(settings: settings, builder: builder);
      },
      home: widget.home,
      routes: widget.routes,
      initialRoute: widget.initialRoute,
      onGenerateRoute: widget.onGenerateRoute,
      onGenerateInitialRoutes: widget.onGenerateInitialRoutes,
      onUnknownRoute: widget.onUnknownRoute,
      builder: _materialBuilder,
      title: widget.title,
      onGenerateTitle: widget.onGenerateTitle,
      textStyle: _errorTextStyle,
      color: materialColor,
      locale: widget.locale,
      localizationsDelegates: _localizationsDelegates,
      localeResolutionCallback: widget.localeResolutionCallback,
      localeListResolutionCallback: widget.localeListResolutionCallback,
      supportedLocales: widget.supportedLocales,
      showPerformanceOverlay: widget.showPerformanceOverlay,
      checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages,
      checkerboardOffscreenLayers: widget.checkerboardOffscreenLayers,
      showSemanticsDebugger: widget.showSemanticsDebugger,
      debugShowCheckedModeBanner: widget.debugShowCheckedModeBanner,
      inspectorSelectButtonBuilder: _inspectorSelectButtonBuilder,
      shortcuts: widget.shortcuts,
      actions: widget.actions,
    );
  }

  @override
  Widget build(BuildContext context) {
    Widget result = _buildWidgetApp(context);

    assert(() {
      if (widget.debugShowMaterialGrid) {
        result = GridPaper(
          color: const Color(0xE0F9BBE0),
          interval: 8.0,
          divisions: 2,
          subdivisions: 1,
          child: result,
        );
      }
      return true;
    }());

    return ScrollConfiguration(
      behavior: _MaterialScrollBehavior(),
      child: HeroControllerScope(
        controller: _heroController,
        child: result,
      )
    );
  }
}